JP-A 56-147740 describes a process for producing 2-(1-hydroxyalkyl)cycloalkanone wherein a cycloalkanone and an alkyl aldehyde are subjected to aldol condensation by using a basic catalyst in an amount of about 0.05 to 0.1 mol per mol of alkyl aldehyde, and JP-A 2001-335529 describes a process for producing the same by aldol condensation using a basic catalyst in an amount of 0.04 mol or less per mole of alkyl aldehyde.
However, the alkyl aldehyde is inherently easily oxidized to form an alkylcarboxylic acid, and this alkylcarboxylic acid is reacted with the basic catalyst during aldol condensation to reduce the catalytic activity significantly, thus significantly lowering the yield and selectivity in many cases. For preventing such oxidation, a method of storing and using the alkyl aldehyde by sealing with nitrogen is adopted, but oxidation proceeds gradually to make contamination with an alkylcarboxylic acid inevitable.
In the processes described in JP-A 56-147740 and JP-A 2001-335529 supra, a cycloalkanone is used in excess of an alkyl aldehyde, and thus the unreacted cycloalkanone remains after the reaction. The cycloalkanone is dissolved in a large amount in the aqueous layer used in the reaction so that if the aqueous layer is discarded after one reaction, the unreacted remaining cycloalkanone will be lost in a large amount, thus increasing an environmental impact.